My Cakewalk is doing exactly this and I want to get rid of it. I don´t remember when it started, but I did not had this "problem" but after one of the updates of octuber, I started getting this issue that all midi instruments would play the same notes, even if there is no midi information on a midi track.
For example, I have one song with 4 midi instruments, 3 Synths Pads and one with drums. For some reason Cakewalk started playing all the midi patterns on all instruments. I was able to change that by selecting a specific channel on the MIDI section of each instrument, but when I export the cakewalk session, it exports the same midi pattern on all midi instruments. Even though when doing playback in the cakewalk session it did not do this.
I attach an image with the setup on cakewalk and sound samples of the result I get.
Any ideas what is happening?